A large percentage of the world's vehicles run on gasoline using an internal combustion engine. The use of such vehicles, more specifically the use of vehicles which rely on fossil fuels, e.g., gasoline, creates two problems. First, due to the finite size and limited regional availability of such fuels, major price fluctuations and a generally upward pricing trend in the cost of gasoline are common, both of which can have a dramatic impact at the consumer level. Second, fossil fuel combustion is one of the primary sources of carbon dioxide, a greenhouse gas, and thus one of the leading contributors to global warming. Accordingly, considerable effort has been spent on finding alternative drive systems for use in both personal and commercial vehicles.
Electric vehicles, due to their cleaner and more efficient drive systems, offer one of the most promising alternatives to vehicles that use internal combustion drive trains. To be successful, however, an electric vehicle must meet consumers' expectations relative to performance, range, reliability, lifetime and cost. These expectations, in turn, place considerable importance on the design, configuration and implementation of the electric vehicle's rechargeable batteries. Clearly a critical aspect of the rechargeable batteries, especially from a consumer's point of view, is the ease and dependability by which the batteries may be recharged, either at home, work or at a public charging station.
Often when discussing the transition between a society dependent upon combustion vehicles and one that relies heavily on electric vehicles, the discussion turns to the need for a charging infrastructure that would make it easy for the electric vehicle owner to charge their vehicle when they are away from their primary charging station (e.g., home charging station). Unfortunately, the current charging infrastructure is quite limited. For example, in a large parking lot or structure, at best there may be one or two parking stalls that provide access to a charging system for recharging an electric vehicle's batteries. While this situation may be adequate for the current number of electric vehicles, as electric vehicles gain wider acceptance the need for better charging station access will become more essential.
FIG. 1 illustrates one method that is intended to increase charging station accessibility in a large parking lot. In this approach, charging stations are located throughout the parking lot such that each charging station is within reach of multiple parking stalls. For example, in the illustrated portion of parking lot 100, three charging stations 101-103 are spread throughout the twelve illustrated parking stalls, thereby allowing each charging station to be in range of four different stalls, i.e., charging station 101 is within range of stalls 1, 2, 7 and 8; charging station 102 is within range of stalls 3, 4, 9 and 10; and charging station 103 is within range of stalls 5, 6, 11 and 12.
Central localization of charging stations within a parking lot or structure as illustrated in FIG. 1 provides physical access to a single charging source by multiple vehicles, significantly increasing accessibility and therefore user convenience. Further improvement may be gained if each charging system 101-103 includes multiple ports, thus allowing simultaneous charging of multiple vehicles. As illustrated in FIG. 2, in a conventional multiport system simultaneous charging is accomplished by incorporating four charging circuits 201-204 within the single system 205. Charging circuits 201-204 are coupled to source 207 (e.g., power grid) and coupled to different vehicle ports 209-212, respectively. In a conventional multiport charging station, charging circuits 201-204 are independent of one another, i.e., the operation or power output of one charging circuit does not impact the operation or power output of the other charging circuits within charging station 205. While this approach may be used to significantly improve vehicle access to a charging source, it is a relatively inefficient and costly approach due to the duplication of charging circuits 201-204. Accordingly, what is needed is an efficient way of simultaneously charging multiple vehicles from a single charging station. The present invention provides such a charging system.